1. Field of the Invention
The present invention concerns a rapid low-pressure casting installation.
2. Description of the Prior Art
It is known that at present, a low-pressure casting installation of an industrial kind comprises 3 elements:
A MAINTAINING FURNACE CONTAINING A FLUID-TIGHT CRUCIBLE CAPABLE OF WITHSTANDING PRESSURES OF 1 TO 1.5 BARS;
A PNEUMATIC MEANS ENSURING THE UPWARD CONVEYING OF THE METAL TOWARDS THE FURNACE EITHER BY GAS OR AIR PRESSURE OR BY DEPRESSION; AND
A CONTACT AND INTERCONNECTION MEANS COMPRISING THE SUPPLY PIPE FOR BRINGING THE MOLTEN METAL FROM THE CRUCIBLE TO THE MOULD AND THE DEVICE FOR THE CENTRING AND FLUID-TIGHT CONTACT BETWEEN THAT PIPE AND THE INPUT ORIFICE OF THE MOULD.
A great step has been made in the improving of low-pressure casting installations when it was possible to substitute an electromagnetic pump for pneumatic means thus making it possible to ensure the upward conveying of the liquid metal towards the mould and thus to avoid enclosing all or a part of the crucible containing the molten metal in a fluid-tight enclosure.
It was thus possible to effect the filling of the mould more regularly, then to bring the forging pressure up to values twice as great as those previously obtained, since the solidity of the walls of the crucible was no longer affected. With forging pressures in the order of 3 bars, it was possible to obtain by that method cast parts having a fineness which it was impossible to obtain up till then by conventional low-pressure casting methods. Low-pressure casting installations using immersed electromagnetic pumps have therefore made it possible to obtain a certain number of improvements. More particularly, it is now easy to regulate the injection speed and the forging overpressure by varying simply the service tension of the pump. The electromagnetic pump can also be fitted to any furnace, providing that it is fitted with a tank in which the pump can be inserted. Thus, the use of overpressure gases with all the leakages which they cause is avoided. Lastly, it is now possible to re-load the furnace while the installation is in service and to insert therein products for refining the metal without interrupting the operation of the installation.
Nevertheless, despite the various improvements exposed hereinabove, low-pressure casting remains an expensive operation requiring the use of expensive machines which remain unused during the cooling time of the moulds and during the refractory washing thereof. The inventor has sought to reduce the stoppage time of the pump during those periods. It is known, indeed, that on referring to the diagram of the operations, the contact and interconnection operation of the pump and the mould, followed by the putting of that mould under pressure and followed by the maintaining of the pressure until the moment when the base of the mould is fixed, represent fairly a time substantially equal to the complete solidifying and cooling time of the part cast in the mould, followed by the time necessary for the removing of the cast part, the subsequent refractory washing time of the mould and the positioning of the cores. In this way, the inventor has observed that the electromagnetic pump remains in general, unused during half the casting cycle. Making use of the specific properties of immersed electromagnetic pumps, it appeared an advantage to make the pump go through a rotation of nearly 180.degree. after a casting operation and to proceed with a second casting operation on a second mould placed at the same distance from the pump during the cooling of the first mould. Such an operation is naturally possible only if a certain number of modifications have been made to the mould, to the molten metal supply pipe, to the means for centring those two elements and to their fluid-tight contact; it being compulsory for these operations to be effected in a very short period of time not causing any extra stoppage.